myself as of 3 hours ago.

1. Get an arduino or similar, install the ArduinoISP sketch
2. Connect the two as described here: https://www.arduino.cc/en/Tutorial/ArduinoToBreadboard
3. Change the board to Arduino Pro or Pro Mini, Processor to 3.3V, 8Mhz, Programmer: Arduino as ISP
4. Hit burn bootloader button
5. Load up the sketch that you want on the device
6. Without changing anything, use "Upload using programmer"
7. Remove arduino, fix wiring changes required to use as programmer

Committed to Electronics Stackexchange for posterity. Or so I can find it when I forget next time...

myself as of 3 hours ago.

1. Get an arduino or similar, install the ArduinoISP sketch
2. Connect the two as described here.
3. Change the board to Arduino Pro or Pro Mini, Processor to 3.3V, 8Mhz, Programmer: Arduino as ISP
4. Hit burn bootloader button
5. Load up the sketch that you want on the device
6. Without changing anything, use "Upload using programmer"
7. Remove arduino, fix wiring changes required to use as programmer

Committed to Electronics Stackexchange for posterity. Or so I can find it when I forget next time...